Dynamics of specific antibody responses induced in mallards after infection by or immunization with low pathogenicity avian influenza viruses

Natural infections with different subtypes of low pathogenicity avian influenza viruses (LPAIVs) are very common in wild duck populations. Recent outbreaks of high pathogenicity avian influenza virus (HPAIV) H5N1 in Eurasian and African countries stimulated monitoring activities in aquatic wild bird populations. Surveillance mainly focused on virus detection. Only a few serologic investigations have been conducted so far, although such data may retrospectively elucidate epidemiologic patterns of different AIV subtypes in the populations under study. To better understand the immunologic and serologic reactions of mallards after infection with LPAIV, we investigated the AIV type- and subtype-specific antibody dynamics in mallards after different LPAIV infections by hemagglutination inhibition, competitive enzyme-linked immunosorbent assay, and western blot analysis, as appropriate. Four groups of mallard ducks were used: 1) naturally infected birds, 2) birds that were experimentally infected with LPAIV, 3) birds that were immunized with inactivated virus preparations, and 4) negative control birds. Ducks were monitored for up to 15 mo, and serum samples were investigated every 1-4 wk. It could be shown that infection with LPAIV in mallards can be traced serologically over prolonged periods of time.